Cell-specific reference signal interference averaging

ABSTRACT

Aspects of the present disclosure provide techniques and apparatus for enhancing performance by selectively applying averaging to CSI reporting processes. According to certain aspects, a base station (e.g., an eNB) with knowledge of traffic patterns of potentially interfering transmitters may signal a UE how (or whether) to apply averaging, for example, when reporting CSI based on interference measurement resources (IMR).

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

This application is a Continuation of U.S. application Ser. No.14/161,312, filed Jan. 22, 2014, and claims the benefit of U.S.Provisional Patent Application Ser. No. 61/756,901, filed Jan. 25, 2013,both of which are herein incorporated by reference in their entirety.

BACKGROUND I. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to cell-specific reference signal(CRS) interference averaging.

II. Background

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) including LTE-Advanced systemsand orthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless terminals.Each terminal communicates with one or more base stations viatransmissions on the forward and reverse links. The forward link (ordownlink) refers to the communication link from the base stations to theterminals, and the reverse link (or uplink) refers to the communicationlink from the terminals to the base stations. This communication linkmay be established via a single-input single-output, multiple-inputsingle-output or a multiple-input multiple-output (MIMO) system.

SUMMARY

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to cell-specific reference signal(CRS) interference averaging.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a user equipment (UE). The method generally includesreceiving, from a base station, an indication of a type of averaging tobe applied for channel state information (CSI) reporting, measuringreference signals received in one or more subframes, generating a CSIreport based on the measurements and the indicated type of averaging,and sending the CSI report.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a base station (BS). The method generally includestransmitting, to a user equipment (UE), an indication of a type ofaveraging to be applied for channel state information (CSI) reportingand receiving, from the UE, a CSI report generated based on referencesignal measurements and the indicated type of averaging.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes means for receiving, from a base station, anindication of a type of averaging to be applied for channel stateinformation (CSI) reporting, means for measuring reference signalsreceived in one or more subframes, means for generating a CSI reportbased on the measurements and the indicated type of averaging, and meansfor sending the CSI report.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a base station (BS). The apparatus generallyincludes means for transmitting, to a user equipment (UE), an indicationof a type of averaging to be applied for channel state information (CSI)reporting and means for receiving, from the UE, a CSI report generatedbased on reference signal measurements and the indicated type ofaveraging.

Certain aspects of the present disclosure also provide apparatuses andprogram products for performing the operations described above.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective aspects.

FIG. 1 is a block diagram conceptually illustrating an example wirelesscommunication network, in accordance with certain aspects of the presentdisclosure.

FIG. 2 is a block diagram conceptually illustrating an example of anevolved node B (eNB) in communication with a user equipment (UE) in awireless communications network, in accordance with certain aspects ofthe present disclosure.

FIG. 3 is a block diagram conceptually illustrating an example framestructure for a particular radio access technology (RAT) for use in awireless communications network, in accordance with certain aspects ofthe present disclosure.

FIG. 4 illustrates an example subframe format for the downlink withnormal cyclic prefix (CP), in accordance with certain aspects of thepresent disclosure.

FIGS. 5-8 illustrate an example gains achieved with channel stateinformation (CSI) filtering, in accordance with certain aspects of thepresent disclosure.

FIGS. 9-10 illustrate example CQI histograms, in accordance with certainaspects of the present disclosure.

FIG. 11 illustrates example operations which may be performed by a UE,in accordance with certain aspects of the present disclosure.

FIG. 12 illustrates example operations which may be performed by basestation (BS), in accordance with certain aspects of the presentdisclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques and apparatus forenhancing performance by selectively applying averaging to CSI reportingprocesses. According to certain aspects, a base station (e.g., an eNB)with knowledge of traffic patterns of potentially interferingtransmitters may signal a UE how (or whether) to apply averaging, forexample, when reporting CSI based on interference measurement resources(IMR). As a result, the report may provide a more useful measurement ofactual interference.

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any aspect described herein as “exemplary”is not necessarily to be construed as preferred or advantageous overother aspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3 GPP2).

Single carrier frequency division multiple access (SC-FDMA) is atransmission technique that utilizes single carrier modulation at atransmitter side and frequency domain equalization at a receiver side.The SC-FDMA has similar performance and essentially the same overallcomplexity as those of OFDMA system. However, SC-FDMA signal has lowerpeak-to-average power ratio (PAPR) because of its inherent singlecarrier structure. The SC-FDMA has drawn great attention, especially inthe uplink communications where lower PAPR greatly benefits the mobileterminal in terms of transmit power efficiency. It is currently aworking assumption for uplink multiple access scheme in the 3GPP LTE andthe Evolved UTRA.

A base station (“BS”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), Evolved NodeB (eNodeB), BaseStation Controller (“BSC”), Base Transceiver Station (“BTS”), BaseStation (“BS”), Transceiver Function (“TF”), Radio Router, RadioTransceiver, Basic Service Set (“BSS”), Extended Service Set (“ESS”),Radio Base Station (“RBS”), or some other terminology.

A user equipment (UE) may comprise, be implemented as, or known as anaccess terminal, a subscriber station, a subscriber unit, a remotestation, a remote terminal, a mobile station, a user agent, a userdevice, user equipment, a user station, or some other terminology. Insome implementations, mobile station may comprise a cellular telephone,a cordless telephone, a Session Initiation Protocol (“SIP”) phone, awireless local loop (“WLL”) station, a personal digital assistant(“PDA”), a handheld device having wireless connection capability, aStation (“STA”), or some other suitable processing device connected to awireless modem. Accordingly, one or more aspects taught herein may beincorporated into a phone (e.g., a cellular phone or smart phone), acomputer (e.g., a laptop), a portable communication device, a portablecomputing device (e.g., a personal data assistant), an entertainmentdevice (e.g., a music or video device, or a satellite radio), a globalpositioning system device, or any other suitable device that isconfigured to communicate via a wireless or wired medium. In someaspects, the node is a wireless node. Such wireless node may provide,for example, connectivity for or to a network (e.g., a wide area networksuch as the Internet or a cellular network) via a wired or wirelesscommunication link.

The techniques described herein may be used for the wireless networksand radio technologies mentioned above as well as other wirelessnetworks and radio technologies. For clarity, certain aspects of thetechniques are described below for LTE, and LTE terminology is used inmuch of the description below.

An Example Wireless Communication Systems

FIG. 1 shows a wireless communication network 100, which may be an LTEnetwork or some other wireless network. Wireless network 100 may includea number of evolved Node Bs (eNBs) 110 and other network entities. AneNB is an entity that communicates with user equipments (UEs) and mayalso be referred to as a base station, a Node B, an access point (AP),etc. Each eNB may provide communication coverage for a particulargeographic area. In 3GPP, the term “cell” can refer to a coverage areaof an eNB and/or an eNB subsystem serving this coverage area, dependingon the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a closed subscriber group (CSG)). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a pico cell may be referred to asa pico eNB. An eNB for a femto cell may be referred to as a femto eNB ora home eNB (HeNB). In the example shown in FIG. 1, an eNB 110 a may be amacro eNB for a macro cell 102 a, an eNB 110 b may be a pico eNB for apico cell 102 b, and an eNB 110 c may be a femto eNB for a femto cell102 c. An eNB may support one or multiple (e.g., three) cells. The terms“eNB”, “base station,” and “cell” may be used interchangeably herein.

Wireless network 100 may also include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (e.g., an eNB or a UE) and send a transmission of the data to adownstream station (e.g., a UE or an eNB). A relay station may also be aUE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 d may communicate with macro eNB 110 a and aUE 120 d in order to facilitate communication between eNB 110 a and UE120 d. A relay station may also be referred to as a relay eNB, a relaybase station, a relay, etc.

Wireless network 100 may be a heterogeneous network that includes eNBsof different types, e.g., macro eNBs, pico eNBs, femto eNBs, relay eNBs,etc. These different types of eNBs may have different transmit powerlevels, different coverage areas, and different impact on interferencein wireless network 100. For example, macro eNBs may have a hightransmit power level (e.g., 5 to 40 W) whereas pico eNBs, femto eNBs,and relay eNBs may have lower transmit power levels (e.g., 0.1 to 2 W).

A network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with the eNBs via a backhaul. The eNBs may also communicatewith one another, e.g., directly or indirectly via a wireless orwireline backhaul.

UEs 120 (e.g., 120 a, 120 b, 120 c) may be dispersed throughout wirelessnetwork 100, and each UE may be stationary or mobile. A UE may also bereferred to as an access terminal, a terminal, a mobile station (MS), asubscriber unit, a station (STA), etc. A UE may be a cellular phone, apersonal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a laptop computer, a cordlessphone, a wireless local loop (WLL) station, a tablet, a smart phone, anetbook, a smartbook, etc.

FIG. 2 is a block diagram of a design of base station/eNB 110 and UE120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. Base station 110 may be equipped with T antennas 234 a through234 t, and UE 120 may be equipped with R antennas 252 a through 252 r,where in general T≥1 and R≥1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCSs) for each UE based on channel quality indicators(CQIs) received from the UE, process (e.g., encode and modulate) thedata for each UE based on the MCS(s) selected for the UE, and providedata symbols for all UEs. Transmit processor 220 may also process systeminformation (e.g., for semi-static resource partitioning information(SRPI), etc.) and control information (e.g., CQI requests, grants, upperlayer signaling, etc.) and provide overhead symbols and control symbols.Processor 220 may also generate reference symbols for reference signals(e.g., the common reference signal (CRS)) and synchronization signals(e.g., the primary synchronization signal (PSS) and secondarysynchronization signal (SSS)). A transmit (TX) multiple-inputmultiple-output (MIMO) processor 230 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, the overheadsymbols, and/or the reference symbols, if applicable, and may provide Toutput symbol streams to T modulators (MODs) 232 a through 232 t. Eachmodulator 232 may process a respective output symbol stream (e.g., forOFDM, etc.) to obtain an output sample stream. Each modulator 232 mayfurther process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal. Tdownlink signals from modulators 232 a through 232 t may be transmittedvia T antennas 234 a through 234 t, respectively.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 and/or other base stations and may providereceived signals to demodulators (DEMODs) 254 a through 254 r,respectively. Each demodulator 254 may condition (e.g., filter, amplify,downconvert, and digitize) its received signal to obtain input samples.Each demodulator 254 may further process the input samples (e.g., forOFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtainreceived symbols from all R demodulators 254 a through 254 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 258 may process (e.g., demodulateand decode) the detected symbols, provide decoded data for UE 120 to adata sink 260, and provide decoded control information and systeminformation to a controller/processor 280. A channel processor maydetermine reference signal received power (RSRP), received signalstrength indicator (RSSI), reference signal received quality (RSRQ),CQI, etc.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (e.g., forreports comprising RSRP, RSSI, RSRQ, CQI, etc.) fromcontroller/processor 280. Processor 264 may also generate referencesymbols for one or more reference signals. The symbols from transmitprocessor 264 may be precoded by a TX MIMO processor 266 if applicable,further processed by modulators 254 a through 254 r (e.g., for SC-FDM,OFDM, etc.), and transmitted to base station 110. At base station 110,the uplink signals from UE 120 and other UEs may be received by antennas234, processed by demodulators 232, detected by a MIMO detector 236 ifapplicable, and further processed by a receive processor 238 to obtaindecoded data and control information sent by UE 120. Processor 238 mayprovide the decoded data to a data sink 239 and the decoded controlinformation to controller/processor 240. Base station 110 may includecommunication unit 244 and communicate to network controller 130 viacommunication unit 244. Network controller 130 may include communicationunit 294, controller/processor 290, and memory 292.

Controllers/processors 240 and 280 may direct the operation at basestation 110 and UE 120, respectively. Processor 240 and/or otherprocessors and modules at base station 110, and/or processor 280 and/orother processors and modules at UE 120, may perform or direct processesfor the techniques described herein. Memories 242 and 282 may store dataand program codes for base station 110 and UE 120, respectively. Ascheduler 246 may schedule UEs for data transmission on the downlinkand/or uplink.

When transmitting data to the UE 120, the base station 110 may beconfigured to determine a bundling size based at least in part on a dataallocation size and precode data in bundled contiguous resource blocksof the determined bundling size, wherein resource blocks in each bundlemay be precoded with a common precoding matrix. That is, referencesignals (RSs) such as UE-RS and/or data in the resource blocks may beprecoded using the same precoder. The power level used for the UE-RS ineach resource block (RB) of the bundled RBs may also be the same.

The UE 120 may be configured to perform complementary processing todecode data transmitted from the base station 110. For example, the UE120 may be configured to determine a bundling size based on a dataallocation size of received data transmitted from a base station inbundles of contiguous RBs, wherein at least one reference signal inresource blocks in each bundle are precoded with a common precodingmatrix, estimate at least one precoded channel based on the determinedbundling size and one or more RSs transmitted from the base station, anddecode the received bundles using the estimated precoded channel.

FIG. 3 shows an exemplary frame structure 300 for FDD in LTE. Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames. Each radio frame may have apredetermined duration (e.g., 10 milliseconds (ms)) and may bepartitioned into 10 subframes with indices of 0 through 9. Each subframemay include two slots. Each radio frame may thus include 20 slots withindices of 0 through 19. Each slot may include L symbol periods, e.g.,seven symbol periods for a normal cyclic prefix (as shown in FIG. 2) orsix symbol periods for an extended cyclic prefix. The 2L symbol periodsin each subframe may be assigned indices of 0 through 2L−1.

In LTE, an eNB may transmit a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) on the downlink in the center1.08 MHz of the system bandwidth for each cell supported by the eNB. ThePSS and SSS may be transmitted in symbol periods 6 and 5, respectively,in subframes 0 and 5 of each radio frame with the normal cyclic prefix,as shown in FIG. 3. The PSS and SSS may be used by UEs for cell searchand acquisition. The eNB may transmit a cell-specific reference signal(CRS) across the system bandwidth for each cell supported by the eNB.The CRS may be transmitted in certain symbol periods of each subframeand may be used by the UEs to perform channel estimation, channelquality measurement, and/or other functions. The eNB may also transmit aphysical broadcast channel (PBCH) in symbol periods 0 to 3 in slot 1 ofcertain radio frames. The PBCH may carry some system information. TheeNB may transmit other system information such as system informationblocks (SIBs) on a physical downlink shared channel (PDSCH) in certainsubframes. The eNB may transmit control information/data on a physicaldownlink control channel (PDCCH) in the first B symbol periods of asubframe, where B may be configurable for each subframe. The eNB maytransmit traffic data and/or other data on the PDSCH in the remainingsymbol periods of each subframe.

The PSS, SSS, CRS, and PBCH in LTE are described in 3GPP TS 36.211,entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation,” which is publicly available.

FIG. 4 shows two example subframe formats 410 and 420 for the downlinkwith a normal cyclic prefix. The available time frequency resources forthe downlink may be partitioned into resource blocks. Each resourceblock may cover 12 subcarriers in one slot and may include a number ofresource elements. Each resource element may cover one subcarrier in onesymbol period and may be used to send one modulation symbol, which maybe a real or complex value.

Subframe format 410 may be used for an eNB equipped with two antennas. ACRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7,and 11. A reference signal is a signal that is known a priori by atransmitter and a receiver and may also be referred to as pilot. A CRSis a reference signal that is specific for a cell, e.g., generated basedon a cell identity (ID). In FIG. 4, for a given resource element withlabel Ra, a modulation symbol may be transmitted on that resourceelement from antenna a, and no modulation symbols may be transmitted onthat resource element from other antennas. Subframe format 420 may beused for an eNB equipped with four antennas. A CRS may be transmittedfrom antennas 0 and 1 in symbol periods 0, 4, 7, and 11 and fromantennas 2 and 3 in symbol periods 1 and 8. For both subframe formats410 and 420, a CRS may be transmitted on evenly spaced subcarriers,which may be determined based on cell ID. Different eNBs may transmittheir CRSs on the same or different subcarriers, depending on their cellIDs. For both subframe formats 410 and 420, resource elements not usedfor the CRS may be used to transmit data (e.g., traffic data, controldata, and/or other data).

An interlace structure may be used for each of the downlink and uplinkfor FDD in LTE. For example, Q interlaces with indices of 0 through Q−1may be defined, where Q may be equal to 4, 6, 8, 10, or some othervalue. Each interlace may include subframes that are spaced apart by Qframes. In particular, interlace q may include subframes q, q+Q, q+2Q,etc., where q∈{0, . . . , Q−1}.

The wireless network may support hybrid automatic retransmission request(HARQ) for data transmission on the downlink and uplink. For HARQ, atransmitter (e.g., an eNB 110) may send one or more transmissions of apacket until the packet is decoded correctly by a receiver (e.g., a UE120) or some other termination condition is encountered. For synchronousHARQ, all transmissions of the packet may be sent in subframes of asingle interlace. For asynchronous HARQ, each transmission of the packetmay be sent in any subframe.

A UE may be located within the coverage of multiple eNBs. One of theseeNBs may be selected to serve the UE. The serving eNB may be selectedbased on various criteria such as received signal strength, receivedsignal quality, path loss, etc. Received signal quality may bequantified by a signal-to-interference-plus-noise ratio (SINR), or areference signal received quality (RSRQ), or some other metric. The UEmay operate in a dominant interference scenario in which the UE mayobserve high interference from one or more interfering eNBs.

Example Cell-Specific Reference Signal Interference Averaging

In certain systems (e.g., long term evolution (LTE) Release 11), channelstate information-interference measurement (CSI-IM) resources can assistthe user equipment (UE) for better interference estimation andmeasurements. The measurement interval for CSI-IM resources may be a UEimplementation.

When the interference is measured based on resources occupied by theinterferer's data transmission, the measurement can show wide variationaccording to the interferer's traffic load. In this case, the measuredinterference may not be well correlated with the interference in aparticular scheduled subframe. To reduce the discrepancy caused by theinterference variations, it is beneficial for the UE to average themeasured interference.

However, in a system where the scheduler is aware of the interferer'straffic pattern, the measured interference can be well correlated withscheduled subframes by associating measurement subframes with schedulingsubframes that are experiencing the same type of interfering traffic. Inthis case, it is not beneficial to average measured interference by theUE.

Since the UE cannot determine itself whether the scheduler (eNB) isaware of the interferer's traffic, the UE is not able to determine thebest averaging strategy without assistance from the eNB.

Therefore, according to certain aspects of the present disclosure, abase station (eNB) may provide a UE with an indication of a type ofaveraging (and/or whether to average). In some embodiments, the eNB maysend signaling to indicate what type of averaging should be followed bythe UE for the CSI report. The averaging may refer to one or more of thefollowing: interference averaging, channel averaging, signal-to-noiseratio (SNR) averaging, and spectral efficiency averaging.

The averaging type can indicate either or both of time-domain averagingand frequency-domain averaging. The signaling may be either dedicated orbroadcast, with dedicated signaling possibly being more efficient andflexible.

An efficient signaling can be a single bit indication, indicating one oftwo different averaging modes. For example, a single bit may indicatethe UE should use a limited, fixed averaging (e.g., one subframe or onephysical resource block (PRB)) or a less restricted (or unrestricted)averaging.

According to certain aspects, for CSI-IM, interference may be measuredon specific resources signaled to the UE. When the CSI report indicatesthat periodicity and timing can be aligned with the CSI-IM resources ofinterest, no further signaling beyond the averaging indication may beused. However, this may introduce undue restriction, for example, the UEreport may be restricted to specific subframes only.

According to certain aspects, the eNB may send additional signaling toassociate a reporting process with a certain set of measurementresources, thereby decoupling the time of measurement from the time ofsending the report.

According to certain aspects, a periodic CSI measurement process may beassociated with a measurement subframe subset by radio resource control(RRC) signaling. In aspects, the averaging indicator may further controlwhether the UE should average within the subframe subset or not.

For CRS-based modes, FIGS. 5-8 illustrates example gains which may beachieved with CSI filtering for UE link level simulations, in accordancewith certain aspects of the present disclosure. FIGS. 5-8 show physicaldownlink shared channel (PDSCH) throughput versus SNR for 1 cell TM2serving 500, 1 cell TM6 serving 600, 2 cell TM2 serving 700, and 2 cellTM6 serving 800, respectively. One curve each graph shows gains with CSIfiltering 502, 602, 702, 802 and the other curve shows gains without CSIfiltering 504, 604, 704, 804. FIGS. 5-8 show example link levelsimulation results for additive white Gaussian noise (AWGN) and explicitinterferer with 50% loading. It can be seen that interferer filtering(in time domain) increases the performance drastically. Frequency domainfiltering is fixed for all scenarios.

In the case of AWGN interferer, filtering may account for channelvariations and help reduce the SNR (CQI) variance. This may help inpreventing overshooting the CQI with higher block error rate (BLER) andlower overall performance. In the case of an explicit interferer,filtering may reduce the variance of SNR (CQI) and prevents CQIovershooting. In the 50% loading case, it may reduce channel andinterference variations.

FIGS. 9 and 10 illustrate example CQI histograms for one cell TM2serving 900 and two cell TM2 serving 1000, in accordance with certainaspects of the present disclosure. FIGS. 9 and 10 each include a barshowing gains with CQI filtering and one bar showing gains without CQIfiltering. It can be seen that the high CQI values (which can result inhigh BLER and impact performance) are reduced.

In aspects, using RS-based modes, CSI filtering may reduce the channeland interferer variations and help reduce the SNR (CQI) varianceresulting in fewer instances where the CQI can overshoot increasing theBLER and reducing performance. In aspects, using CSI-RS and CSI-IMmodes, UE may be configured to report multiple CSI reports measuringdifferent interference structures. Filtering CSI in these cases reliesheavily on the level of transmission point coordination.

According to certain aspects, where tight transmission point (TP)coordination is implemented across a large geographical area, UE CSIfiltering may not be used. The interference may be controlled by thenetwork and the UE can rely on this coordination. It may be desirablefor the network to know exactly what interference the UE is seeing perCSI report without any significant time or frequency filtering to betterdecide on TP scheduling. Filtering in these cases may not give thenetwork a true picture of the interference as the CQI can become noisyand not reflective of the latest measurement. In aspects, UE CSIfiltering may not be used for CSI-RS and CSI-IM based modes where tightTP coordination and minimal uncontrolled interference exists.

According to certain aspects, where tight TP coordination is notimplemented or coordinated multipoint (CoMP) cluster size is moderate,UE CSI filtering can help with the performance. In CoMP scenarios 1, 2,3, and 4, the cluster size may be limited to 1, 3, or 9 macro cells;hence, residual interference outside the CoMP cluster could besignificant for many UEs. These UEs can benefit from CSI filtering tocontrol the interference variation. This is similar to the CRS-basedmodes, where CSI filtering increases the performance by reducing thechannel and interferer variations and helps control the SNR and CQI sentto the network.

In aspects, UE CSI filtering may be desirable for CSI-RS and CSI-IMbased modes where tight TP coordination is absent or significantuncontrolled interference exists.

It can be seen that the effect of having or not having UE CSI filteringis not the same in all cases. There might be cases where filtering isnot desirable and cases where it is desirable. This can depend on thecoordination level as well as the network control on the interference.

For CSI-RS and CSI-IM based modes, UE CSI filtering can help in certainscenarios, and may not help in others. In aspects, for CSI-RS/CSI-IMbased modes, the network may signal the filtering behavior to the UEbased on the deployment and the network knowledge of the interferencestructure. This may help the UE in achieving the maximum performance inall conditions. In aspects, the network may send signaling informationto the UE specifying the filtering behavior needed based on thedeployment and the network knowledge of the interference structure.

FIG. 11 illustrates example operations 1100, in accordance with certainaspects of the present disclosure. The operations 1100 may be performed,for example, by a UE. The operations 1100 may begin, at 1102, byreceiving, from a base station, an indication of a type of averaging tobe applied for channel state information (CSI) reporting.

At 1104, the UE may measure reference signals received in one or moresubframes.

At 1106, the UE may generate a CSI report based on the measurements andthe indicated type of averaging and may send the report, at 1008.

FIG. 12 illustrates example operations 1200, in accordance with certainaspects of the present disclosure. The operations 1200 may be performed,for example, by a base station. The operations 1200 may begin, at 1202,by transmitting, to a user equipment (UE), an indication of a type ofaveraging to be applied for channel state information (CSI) reporting.

At 1204, the BS may receive, from the UE, a CSI report generated basedon reference signal measurements and the indicated type of averaging.

As noted above, the indication of what type of averaging to use mayindicate time domain averaging, frequency domain averaging, or noaveraging. Further, the indication may indicate at least one of:interference averaging, channel averaging, signal to noise ratio (SNR)averaging, or spectral efficiency averaging.

The indication may be signaled in various ways. In some cases, theindication may be sent as part of a CSI reporting configuration. In somecases, separate indications may be provided independently for differentinterference measurement resources (IMRs). The indication may beprovided via broadcast or dedicated signaling from the base station.Different indications may be provided for different CSI processes for asame interference measurement resource (IMR).

Further, different indications may be provided for different types ofaveraging to be applied independently to different subsets of subframes.For example, subframes in a subset may be selected based, at least inpart, on traffic load of a corresponding interfering base station.

As described above, the indication may be provided as a single bitindicating one of two averaging modes. The two averaging modes mayinclude a fixed averaging mode wherein averaging is applied across alimited range of resources and a less restricted averaging mode whereinaveraging is applied across a wider range of resources.

In some cases, the indication may associate a reporting process with acertain set of measurement resources. For example, the indication mayassociate a periodic CSI measurement process with a measurement subframesubset.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software/firmwarecomponent(s) and/or module(s), including, but not limited to a circuit,an application specific integrated circuit (ASIC), or processor.Generally, where there are operations illustrated in the Figures, thoseoperations may be performed by any suitable corresponding counterpartmeans-plus-function components.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an example of exemplary approaches. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or combinations thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, software/firmware, or combinations thereof. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software/firmware dependsupon the particular application and design constraints imposed on theoverall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device (PLD), discretegate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in asoftware/firmware module executed by a processor, or in a combinationthereof. A software/firmware module may reside in RAM memory, flashmemory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software/firmware, or combinations thereof. Ifimplemented in software, the functions may be stored on or transmittedover as one or more instructions or code on a computer-readable medium.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer-readable media may comprisenon-transitory computer-readable media (e.g., tangible media). Inaddition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

1. A method for wireless communications by a user equipment (UE),comprising: receiving, from a base station (BS), an indication ofwhether to average channel state information (CSI) measurements over aset of subframes for CSI reporting, the indication being based onoccupancy of the set of subframes; measuring reference signals receivedin the set subframes; generating a CSI report based on the measurementsand the indication of whether averaging should be applied; and sendingthe CSI report.
 2. The method of claim 1, wherein the reference signalscomprise CSI-RS.
 3. The method of claim 1, wherein the averagingcomprises averaging the CSI-RS measurements across the set of subframes.4. The method of claim 1, wherein receiving the indication of whether toaverage comprises receiving an indication of to perform averaging for afirst subset of subframes and an indication not to perform averaging fora second subset of subframes.
 5. The method of claim 4, wherein theindication is based on traffic load in the set of subframes.
 6. Themethod of claim 1, wherein the indication is based on at least one of:level of interference or a level of coordination among transmissionpoints.
 7. The method of claim 1, wherein the indication to averagefurther comprises an indication to average in the time domain, thefrequency domain, or both.
 8. The method of claim 1, wherein theindication to average further comprises an indication of at least oneof: interference averaging, channel averaging, signal to noise ratio(SNR) averaging, or spectral efficiency averaging.
 9. The method ofclaim 1, wherein the indication is received as part of a CSI reportingconfiguration.
 10. The method of claim 1, wherein the indication ofwhether to average is provided as a single bit.
 11. A method forwireless communications by a base station (BS), comprising: sending, toa user equipment (UE), an indication of whether to average channel stateinformation (CSI) measurements over a set of subframes for CSIreporting, the indication being based on occupancy of the set ofsubframes; send reference signals to the UE in the set subframes; andreceive a CSI report from the UE based on the indication.
 12. The methodof claim 11, wherein the reference signals comprise CSI-RS.
 13. Themethod of claim 11, wherein the averaging comprises averaging the CSI-RSmeasurements across the set of subframes.
 14. The method of claim 11,wherein sending the indication of whether to average comprises sendingan indication of to perform averaging for a first subset of subframesand an indication not to perform averaging for a second subset ofsubframes.
 15. The method of claim 14, wherein the indication is basedon traffic load in the set of subframes.
 16. The method of claim 11,wherein the indication is based on at least one of: level ofinterference or a level of coordination among transmission points. 17.The method of claim 11, wherein the indication to average furthercomprises an indication to average in the time domain, the frequencydomain, or both.
 18. The method of claim 11, wherein the indication toaverage further comprises an indication of at least one of: interferenceaveraging, channel averaging, signal to noise ratio (SNR) averaging, orspectral efficiency averaging.
 19. The method of claim 11, wherein theindication is sent as part of a CSI reporting configuration.
 20. Themethod of claim 11, wherein the indication of whether to average isprovided as a single bit.
 21. An apparatus for wireless communications,comprising: a memory; and at least one processor coupled with the memoryand configured to: receive an indication of whether to average channelstate information (CSI) measurements over a set of subframes for CSIreporting, the indication being based on occupancy of the set ofsubframes; measure reference signals received in the set subframes;generate a CSI report based on the measurements and the indication ofwhether averaging should be applied; and send the CSI report.
 22. Theapparatus of claim 21, wherein the reference signals comprise CSI-RS.23. The apparatus of claim 21, wherein the averaging comprises averagingthe CSI-RS measurements across the set of subframes.
 24. The apparatusof claim 21, wherein the at least one processor is configured to receivean indication of to perform averaging for a first subset of subframesand an indication not to perform averaging for a second subset ofsubframes.
 25. The apparatus of claim 24, wherein the indication isbased on traffic load in the set of subframes.
 26. A apparatus forwireless communications, comprising: a memory; and at least oneprocessor coupled with the memory and configured to: send an indicationto another apparatus of whether to average channel state information(CSI) measurements over a set of subframes for CSI reporting, theindication being based on occupancy of the set of subframes; sendreference signals to the other apparatus in the set subframes; andreceive a CSI report from the apparatus based on the indication.
 27. Theapparatus of claim 26, wherein the reference signals comprise CSI-RS.28. The apparatus of claim 26, wherein the averaging comprises averagingthe CSI-RS measurements across the set of subframes.
 29. The apparatusof claim 26, wherein sending the indication of whether to averagecomprises sending an indication of to perform averaging for a firstsubset of subframes and an indication not to perform averaging for asecond subset of subframes.
 30. The apparatus of claim 29, wherein theindication is based on traffic load in the set of subframes.